The invention pertains to an apparatus for preventing high-frequency radiation in a cavity from escaping through the covered openings of the cavity.
Measures and apparatuses for providing effective shielding against, and for suppressing the escape of, electromagnetic, high-frequency alternating fields from the cavities surrounding them are known. For example, care must be taken especially in the design of pass-through openings in cavities such as door openings which must be opened and closed at regular intervals to ensure that the shielding elements covering the openings are in good electrical contact with the chamber walls forming the boundaries of the cavity and that no HF leaks are formed between the chamber walls and the shielding devices closing the openings as a result of remaining gaps, for example. Gaps of this type, especially when the size of the gap is equal to .lambda./4 of the wavelength .lambda. of the electromagnetic radiation present, act as slot antennas, through which the electromagnetic radiation to be shielded against can escape very effectively.
High-frequency electrical and/or magnetic alternating fields to be shielded against arise, for example, during the operation of magnetrons, which are used for cathode sputtering and the cathodic coating of surfaces. In these magnetrons, a high-frequency alternating electric field is used to maintain an electrical discharge between the cathode to be sputtered and the anode assigned to it. The typical operating frequencies of these types of cathode sputtering systems can be as high as 40 MHz. Because the cathode sputtering processes occur under vacuum conditions, the process chambers provided for them are frequently made vacuum-tight by means of rubber seals, but they are not always HF-tight in their original condition.
Especially the closable openings in the process chambers which must be provided for upkeep and maintenance, e.g., to replace the sputter cathodes, have turned out to be weak points with respect to HF leakage, especially after they have been opened and closed several times. As a result, the electromagnetic radiation which escapes from such process chambers acts as an interference signal, and because of the high radiation intensities required for the sputtering process, these signals can interfere severely with radio reception.